Solid composite propellants with



wi w ar SOLID COMPOSITE PROBELLANTSIWITH BURNING RATE CATALYST Willard M. St. John, In, Waco, Tex assignor to Phillips Petroleum Company, a corporation of Delaware This invention relates to solid propellants. In one aspect it relates to an improved method for producing solid propellant mixtures comprising a solid oxidant, a rubbery binder material and a burning rate catalyst. In another aspect the invention relates to a novel composition employed in the manufacture of solid propellant mixtures which provides an improvement in the compounding of solid propellant mixtures. In still another aspect it relates to a simplified and improved sequence of steps employed in the manufacture of solid propellants.

Recently it has been discovered that superior solid propellant mixtures are obtained comprising a solid oxidant such as ammonium nitrate or ammonium perchlorate and a rubbery binder material such as a copolymer of butadiene and a vinylpyridine or other substituted heterocyclic nitrogen base compound, which after incorporation is cured by a quaternization reaction or a vulcanization reaction. Solid propellant mixtures of this nature and a process for their production are disclosed and claimed in copending application Serial No. 284,447, filed April 25, 1952, by W. B. Reynolds and J. E. Pritchard.

In the production of solid propellant mixtures of the type hereinbefore disclosed, the ratio of oxidant to binder is usually very high, often about to 9 parts by weight of oxidant to one part by weight of binder material. It is necessary that the rubbery binder of such propellant mixtures be the continuous phase in which the oxidant is dispersed in order to obtain satisfactory consolidation so that upon curing a solid material of substantial structural strength will be obtained. Heretofore, one of the difii- &6.

improved method for producing solid propellants. It is also an object of this invention to provide a sequence of steps whereby the drying step with respect to the solid oxidant and the burning rate catalyst is eliminated in the production of solid propellant mixtures. Another object of this invention is the provision of a method for producing solid propellant mixtures wherein the step of dry blending the solid oxidant and the burning rate catalyst is eliminated. It is stillanother object of this invention to provide a novel composition of ingredients which facili tates the incorporation of a solid oxidant into a rubbery binder. Other objects and advantages of this invention will be apparent to one skilled in the art upon studying this disclosure.

Broadly, the invention relates to an improved method for the manufacture of solid propellants by incorporating a paste comprising a complex cyanide of iron, which is prepared in the presence of a small amount of naphthenic acid, and a plasticizer, into the rubbery binder prior to incorporation therein of the solid oxidant. A surface active agent is preferably utilized in preparing the paste and is removed in drying the paste. The invention also relates to a novel compositioncomprising a complex cyanide of culties encountered in the manufacture of propellants of this type has been that of loss of a continuous phase 'whereby the binder forms a discontinuous phase in the oxidizer. When the continuous phase is lost in this -manner, the batch cannot be used to prepare a propellant charge and must be discarded or reprocessed in some manner. An additional difliculty attnedant with a .mix-

ture having a tendency toward loss of continuous phase *is that the mixing time required to obtain a satisfactory product is greatly extended.

in copending application Serial No. 475,000, filed De- .cember 13, 1954, byH. G. Cutforth, there is'described a :method for preparing solid propellant mixtures of the :nature contemplated in this invention which comprises dry blending the burning rate catalyst and the solid oxidant .prior to its incorporation in the rubber binder material.

This procedure resulted in improved results over the prior art methods of mixing the dry solid oxidant and the rubbery binder over the procedures known heretofore. This procedure, however, requires that both the solid oxidant and the burning rate catalyst be dry when blended together and the burning rate catalyst, which is Milori blue, is subject to dusting during the mixing operation with the result that the equipment and the operators are continually subjected to coloring by-the blue dust evolved from the mixing operation. A V j It is therefore an object of this invention to provide an iron prepared in the presence of a small amount of naphthenic acid and a plasticizer such as dibutoxyethoxyethyl formal, monoamylbiphenyl, benzophenone, liquid polybutadien'e, and the like. Dibutoxyethoxyethyl formal is the preferred plasticizer and it has been found that the commercial grade of this material sometimes contains impurities boiling at less than 190 F., therefore, this material preferably is distilled at a temperature of about 190 F. and atmospheric pressure to remove such impurities. If other plasticizers are used it should be determined that they contain no materials boiling or vaporizing at a temperature below about 190 F.

Oxidants applicable in preparing the solid propellants applicable to the process of this invention are those oxygen-containing solids which readily give up oxygen and include ammonium nitrate, ammonium perchlorate and various other perchlorates, chlorates; dichromates, chromates, and the like. The average particle size of a finely divided oxidant suitable for blending with a catalyst so as to obtain the improvements of this invention should be less than 200 microns and can be from 60 to 200 microns. The amount of solid oxidant uilized is usually a major amount of the total composition and is generally in the range between 50 and weight percent of the total propellant composition. If desired, howeve less than 50 weight percent of the oxidant can be used.

The catalysts which can be used in the practice of this invention include iron cyanide complexes such as Milori blue, Prussian'blue, Chinese blue, and the like, ammonium dichromate, potassium dichromate, ferric oxide, lead oxide, and the like. The average particle size of the finely divided catalyst which can be used to obtain the improvements of'this invention should be less than 40 microns and can be from 0.02 to 40' microns. The amount of catalyst used in preparing propellant compositions according to he method of this invention is usually in the ranged of 7 to 200 parts by weight of, oxidant per part by weight of catalyst. The preferred catalyst for the practice of this invention is Milori blue, which is a highly colored pigment material similar to Prussian blue prepared by the oxidation of a paste of potassium ferrocyanide and ferrous sulfate in the presence of a small amount of naphthenic acid. Electron micrographs at 50,000X of this preferred catalyst show the ultimate particles to be uniform in size, apparently spherical in shape and strung together in short chains." Similar micrographs of Milori blue prepared in the absence of naphthenic acid show ultimate particles which have a more blocky, crystalline appearance and a wide range of ultisurface and rendering the .surfacetcom'patible with 'the plasticizer. Such surface active agents :include Eth'o meens ('ethylene oxide substituted alkyl'amines marketed byfArmour and Co.) Other wetting-agents can be' used and it is preferred that the wetting agen't' be :suchvthat it will beremoved during the'drying'step. i

The copolyrne'rs which a'rens'ed to bind themate'rials of thesolid propellants comprise a conjilgatecl diene:co' ntaining 'fr'onr4 to 8 carbon atoms permolecule such as butadiene, isoprene, piperylene, methylpentadi'e'ne, chloroprene, and the like 'copoly meriz'ed with a polymerizable he'te'rocyclic "nitrogenba's'e such "as the vinylesubstitute'd pyridine's, vinyl substituted nin'olines and various alkylsubstituted derivatives of these compounds such as 2-i 11ethyl5-viny1pylidine (MVP) '2-vinylpyridin e, Z-vinylquinoline and the like. .The copolymers can be'prepared by any suitable method, e.g., emulsion polymerization. It is-often desirable to incorporate carbon black in'the eepoiymer during its preparation. Theaddition of carbon black is accomplished by'conventional'methods, such asfadding the carbon black to the latex prior to coagulation to form a masterbatch, and the amount of carbon blackcan be from 0 to 35 parts of black per lOO'p'arts of :copolyrner. {In'the preparation of the copolymers, the I amount of conjugated diene will beat least 50 parts by 7 weight per 100 parts of the monomer mixture and the 'heterocyclic nitrogen base component will be in the range Sto 50 parts. While the invention isdescribed'herein with particular respect to polymers in which a heterocyclic nitrogen base is included, otherrubberypolymers, such'as butadiene-styrene copolymenare also applicable.

Compounding agents are incorporated into the copolymer in producing the rubberybinder of the propellant compositions prepared according to theprocessoftliis invention. Compounding agents include vulcanization "agents, q'uaterniz ation agents, vulcanization accelerators "softeners, stabilizers such as antioxidants, surface active "agents, etc. 7 V

7 TheMilori blue prepared in the presence ofnaphthenic acid will contain naphthenic acid "in the range of about lf/z to about Z /riWei'ghtperc'ent. V v v p p I Ihecomposition'of a typicalpropellant-manufactured 'by the process of this invention isshownin Table Ijbutfit "is to be understood that the compositioniis exemplary and is not to be construed as limiting the invention.

. Table I Parts Per .Weight Ingredient 100 Parts Percent v Copolymer V I V Butadiene-methylvinylpyridinc 'copolym er 100 12 25 jFiller (narbon'black) Plasticizer- (di-butoxyethoxyethyl formal). "Burning'rate catalyst (Milori blue) "OXidant (ammonium nitrate) Auiiliary ingredientsmayalso be added tothe copoly- -mer binder composition as listed in Table'II.

As 5 species embodiment of. the int/miss the reparation .of .a solid propellant will .be describedhaving the composition shown in Table III.

Table 111 Ingedient Wt. Percent Butadieue-methylvinylpy Dibutoxyethoxyetbyl formal Furnace carbon l k I v I p Flexarnine (A'physical mixture'eontaining fisyg t a'complex diarylaminoketone reaction product .and :N',N in e y rpny dm l Milori blue.-.

The butadiene-methylvinylpyridine copolymer containing-the carbon black wasreceived as=a masterbatch from the .lsupplier. ,The inasterbatch was masticated and the v.plas tici zer east/mart, blue were added in the forniof va previously prepared paste.' The ;paste 'was lprfepar'ed 'by admixing dibutoxyethoxyethyl formal .with Milor'i blue prepared linjthepresence of. naphthenicacid .and containingabout 2 weight percent naphtheni'cacid in the propor- .tioris shown in Table III. QAwttingagent'w'as employed intprepari'ng, thei p aste. and. was removed substantially with the water ,irra ivacuum dryingstepg ,Sorneof the water separated gfronr theplate and was decanted during the above procedure were tired and the results were compared Table 11 V Parts/10o -Ingredient Part5 H 'Bin'der i attingjagent.. O "Antioxidant O. .Suliur a e '0.

Catalyst; Dispersion-;---. I

with results obtainedlby firing propellant-grains prepared according to the procedure of the prior art. All factors, other-than the procedural steps of preparing-thepropellant. composition, were held constant. The data obtained .fromitfiring' these propellant .grains are tabulated :in 'TableIV.

- Table IV Grai a With Paste importer Controlflrslns Burning are i at 1.ooo-......-.,.., o e -V V I e n ri ss Ability ,v. on d Physical Appearance of Grain.

' Satisfactory.

The above: datashowthat, the ballistic; parameters 1 are substantially equal and that the processability. and other characteristics of these compositions are also substantially equal and therefore the process according to this invention provides a defihiteadvantage in the preparation of the 'composition by the elimination'of one step 'in the process,

namely that of dry blending the catalyst andthe'oxidant,

and also avoids dustingof the'personnel and equipment "with the-highly colored burning 'ratecatalyst.

essence.- ofwhich is the Y provision .of an improved procedure'fon the' preparation of solid propellants by incorporating'theburnin'g rate catalyst together with the-plas 'ticizer into' the-binden-material and then-incorporating the,solidoxidant into the binder material. Further'improvements are achieved by preparing a paste of the burning rate catalyst and the plasticizer; removing materials from the di-butoxyethoxyethyl formal which vaporizes at a temperature below 190 F.; and preparing Milori blue as a burning rate catalyst in the presence of a small amount of naphthenic acid.

That which is claimed is:

1. In the method of developing thrust wherein a solid propellant charge contained in a combustion chamber of a rocket motor is ignited and then burned with the evolution of combustion gases which are exhausted from said combustion chamber, the step which comprises burning in said combustion chamber a propellant charge corm prising: as a base propellant, about 50 to 90 weight percent of an inorganic oxidizing salt; and about 50 to about weight percent of a binder comprising a copolymer of a conjugated diene having 4 to 8 carbon atoms per molecule and at least one substituted heterocyclic nitrogen base selected from the group consisting of pyridine, quinoline, an alkyl substituted pyridine and an alkyl substituted quinoline, wherein the total number of carbon atoms in the nuclear alkyl substituents is not more than and wherein R is selected from the group consisting of hydrogen and a methyl radical, 0 to 35 parts of carbon black per 100 parts of copolymer, 10 to 30 parts by Weight per 100 parts copolymer of a plasticizer selected from the group consisting of di-butoxyethoxyethyl formal, monoamylbiphenyl, benzophenone, and liquid polybutadiene, and 10 to 30 parts by weight per 100 parts copolymer of Milori blue prepared in the presence of a sufiicient amount of naphthenic acid so that 1V2 to 2 /2 Weight percent naphthenic acid remains in the Milori blue whereby the particles of Milori blue are spherical in shape, strung together in short chains, and are uniform in size in a range of 0.02 to 40 microns.

2. A composition consisting essentially of 40 to 60 weight percent Milori blue prepared in the presence of a suflicient amount of naphthenic acid so that 1% to 2% weight percent naphthenic acid remains in the Milori blue; and 40 to 60 weight percent di-butoxyethoxyethyl formal.

3. A composition consisting essentially of 40 to 60 weight percent Milori blue prepared in the presence of a suificient amount of naphthenic acid so that 1 /2 to 2 /2 weight percent naphthenic acid remains in the Milori blue; and 40 to 60 weight percent of a plasticizer selected from the group consisting of di-butoxyethoxyethylformal, monoamylbiphenyl,benzophenone, and liquid polybutadiene.

4. A solid propellant composition consisting essentially of about 50 to 90 weight percent of an inorganic oxidizing salt; and about 50 to about 10 weight percent of a binder consisting essentially of a copolymer of a conjugated diene having from 4 to 8 carbon atoms per molecule and at least one substituted heterocyclic nitrogen base selected from the group consisting of pyridine, quinoline, an alkyl substituted pyridine and an alkyl substituted quinoline, wherein the total number of carbon atoms in the nuclear alkyl substituents is not more than 15 and wherein R is selected from the group consisting of hydrogen and a methyl radical, 0 to 35 parts of carbon black per 100 parts copolymer, and 10 to 30 parts by weight per 100 parts copolymer of Milori blue prepared in the presence of a suflicient amount of naphthenic acid so that 1% to 2 /2 weight percent naphthenic acid remains in the Milori blue whereby the particles of Milori blue are spherical in shape, strung together in short chains, and are uniform in size in a range of 0.02 to 40 microns.

5. A solid propellant composition consisting essentially of 50 to 90 weight percent of an inorganic oxidizing salt; and about 50 to about 10 weight percent of a binder consisting essentially of a copolymer of a conjugated diene having 4'to 8 carbon atoms per molecule and at least one substituted-heterocyclic nitrogen base selected from the group consisting of pyridine, quinoline, an alkyl substituted pyridine and an alkyl substituted quinoline, wherein the total number of carbon atoms in the nuclear alkyl substituents is not more than 15 and wherein R is selected from the group consisting ofhydrogen and a methyl radical, 0 to 35 parts of carbon black per 100 parts of copolymer, 10 to 30 parts by weight per 100 parts copolymer of a plasticizer selected from the group consisting of di-butoxyethoxyethyl formal, monoamylbiphenyl, benzophenone, and liquid polybutadiene, and 10 to 30 parts by weight per 100 parts copolymer of Milori blue prepared in the presence of a sufiicient amount of naphthenic acid so that 1% to 2 /2 weight percent naphthenic acid remains in the Milori blue whereby the particles of Milori blue are spherical in shape, strung together in short chains, and are uniform in size in a range of 0.02 to 40 microns.

6. An improved method for preparing an extrudable solid propellant composition comprising an inorganic solid oxidizing salt, a binder comprising a copolymer of a conjugated diene having 4 to 8 carbon atoms per molecule and at least one substituted heterocyclic nitrogen base selected from the group consisting of pyridine, quinoline, an alkyl substituted pyridine and an alkyl substituted quinoline,. wherein the total number of carbon atoms in the nuclearalkyl substituents is not more than 15 and wherein R is selected from the group consisting of hydrogen and a methyl radical, Milori blue prepared in the presence of a suflicient amount of naphthenic acid so that 1 /2 to 2 /2 weight percent naphthenic acid remains in the Milori blue, and a rubber plasticizer, which comprises first admixing the Milori blue and plasticizer to form a paste containing about 40 to 60 Weight percent Milori blue and about 40 to 60 weight percent plasticizer; then admixing said paste with the copolymer binder; and then admixing the solid oxidant with the plasticized binder.

7. In the process of making an extrudable solid propellant composition comprising an inorganic solid oxidizing salt, a binder comprising a copolymer of a conjugated diene having from 4 to 8 carbon atoms per mole-- cule and at least one I emu-n substituted heterocyclic nitrogen base selected from the group consisting of pyridine, quinoline, an alkyl substituted pyridine and an alkyl substituted quinoline, wherein the total number of carbon atoms in the nuclear alkyli. substituents is not more than 15 and wherein R is selori blue, and a rubber plasticizer, the improvement com-- prising first admixing Milori blue and plasticizer to form: a paste containing about 40 to 60 weight percent Milorii blue and about 40 to 60 weight percent plasticizer; then admixing the paste and the copolymer binder; and then admixing the solid oxidant with the copolymer binder so that the binder forms the continuous phase in the re-- sulting composition.

8. The process of claim 7 wherein the oxidizing salt is ammonium nitrate; the binder is a copolymer of buta-- 1 7 diene and methylvinylpyfidine; and the plasticizer is dibutoxyethoxyethyl formal.

V v i Refqrbpces in ih-fildf this ia'aithti" f UNITED STATES PATENTS 2,118,511 Hucks May g4, 1938 2,558,304 Marcot et a1 June 26, 1951 FOREIGN "PATENTS 655,585 Great Britain m 25, 1951 I 

1. IN THE METHOD OF DEVELOPING THRUST WHEREIN A SOLID PROPELLANT CHARGE CONTAINED IN A COMBUSTION CHAMBER OF A ROCKET MOTOR IN IGNITED AND THEN BURNED WITH THE EVOLUTION OF COMBUSTION GASES WHICH ARE EXHAUSTED FROM SAID COMBUSTION CHAMBER, THE STEP WHICH COMPRISES BURNING IN SAID CUMBUSTION CHAMBER A PROPELLANT CHARGE COMPRISING: AS A BASE PROPELLANT, ABOUT 50 TO 90 WEIGHT PERCENT OF AN INORGANIC OXIDIZING SALT: AND ABOUT 50 TO ABOUT 10 WEIGHT PERCENT OF A BINDER COMPRISING A COPOLYMER OF A CONJUGATED DIENE HAVING 4 TO 8 CARBON ATOMS PER MOLECULE AND AT LEAST ONE 